The importance of secondary batteries has been increasing in applications as the on-vehicle electric power sources and the electric power sources for personal computers and mobile information terminals. Regarding such secondary batteries, JP 2001-185225 A (Patent Document 1), for example, discloses a lithium-ion secondary battery in which a plurality of oblong cylindrical-shaped battery elements are enclosed in a battery case so that the side faces of the oblong cylindrical shapes are attached to each other, and a heat releasing member is disposed between the battery case and the battery elements.
An example of the secondary battery that is lightweight and achieves high energy density is a lithium-ion secondary battery. The lithium-ion secondary battery is expected to be used suitably for an on-vehicle high-power electric power source. A typical example of the lithium-ion secondary battery includes positive and negative electrodes each having an electrode active material that can absorb and release lithium ions, a separator disposed between them, and a non-aqueous electrolyte solution. A known example of such a lithium-ion secondary battery has a construction in which an electrode assembly (wound electrode body), made by interposing separators between positive and negative electrode sheets and winding them together, is enclosed in a battery case (battery container) with a non-aqueous electrolyte solution, the electrode assembly. This type of battery is disclosed in, for example, JP 2007-18968 A (Patent Document 2).